Findings from the pooled analysis include:

• Overall, women currently taking OCs or who have quit use within the past 10 years were slightly more likely than nonusers to be diagnosed with breast cancer.
• Risk was greatest for current users and decreased with time between last use and diagnosis. Relative risk was 1.24 for current users, 1.16 for women who had stopped use within one to four years before diagnosis, and 1.07 for women who had stopped use five to nine years before diagnosis.
• There was no additional risk for OC users who discontinued use 10 to 20 years before diagnosis. In some subgroups former OC users faced less risk than nonusers.
• The excess risk of breast cancer diagnoses in OC users was solely for cancers that were localized. OC users actually had a reduced risk of cancers that had spread beyond the breast.
• Women who used OCs before age 20 faced somewhat higher relative risk, when compared with nonusers of the same age, than women who used OCs later in life.
• Whether a woman first used OCs before or after she first gave birth did not appear to make much difference.
• For women with a family history of breast cancer, OC use did not seem to increase risk particularly.
• Duration of OC use did not affect risk.
• Data were limited, but risk did not appear to be related to type of estrogen or progestin, and the only dose-related difference was a reduction in breast cancer among women who had used the highest dose pills more than 10 years before (82, 83).

The relation observed between breast cancer risk and hormone exposure is unusual, and it is not possible to infer from these data whether it is due to an earlier diagnosis of breast cancer in ever-users, the biological effects of hormonal contraceptives, or a combination of reasons. (82)

The finding that the modest additional risk is greatest during OC use and eventually disappears after a woman stops OCs has important public health implications (521). Because most women use OCs when they are young, and breast cancer is extremely rare at young ages, the number of breast cancer cases attributable to OC use would be quite small. By the Collaborative Group's estimate, among 10,000 European or North American women using OCs from ages 16 to 19, an additional 0.5 cases of breast cancer would be diagnosed in the 10 years after these women quit OC use; among those using OCs from ages 20 to 24, 1.5 additional cases; and among those using OCs from ages 25 to 29, 4.7 additional cases. Because of this age gradient, earlier OC use in a population does not lead to more cancers diagnosed overall (82). Generally, the numbers of additional cases would be smaller in developing countries, where breast cancer is less common (83). By 20 years after stopping OC use, there was no significant difference between women who used OCs at these ages and nonusers in the cumulative number of breast cancer cases diagnosed.

Population Services International

A parade float promotes social-marketed Nova brand oral contraceptives and injectables in Pakistan.